Insertion of null packets to mitigate the effects of interference in wireless communications

ABSTRACT

Mitigation of interference effects in certain wireless communications is accomplished by the disclosed method. A wireless communications device communicates utilizing a protocol which requires hopping from channel to channel within a communications frequency band while transmitting. Operating according to the disclosed method, the device scans the available communications channels and identifies channel(s) experiencing interference from other transmitting devices. When hopping to such identified channels, the device transmits only null packets, thus avoiding the need to re-transmit packets due to interference and mitigating the effects of such interference on the communications data rate.

BACKGROUND OF THE INVENTION

[0001] Wireless communications is currently enjoying a period of rapidtechnological advancement and tremendous growth in popularity. In orderto allow wireless communication to become truly convenient andomnipresent, standards have been developed and implemented so that thevarious wireless-enabled devices may readily communicate with oneanother. One such standard has been developed by Bluetooth SIG, Inc.(SIG=“Special Interest Group”), a consortium of companies interested inseeing the growth in wireless networks continue. The standard developedby this group has become known as Bluetooth and devices conforming tothe standard are known as Bluetooth devices or Bluetooth-enableddevices. The Bluetooth standard is based on the IEEE (“Institute ofElectrical and Electronics Engineers”) 802.11b standard and applies to ashort-range radio system designed to replace cables in a personal areanetwork (in the 10 m range). These devices operate in what is known asthe Industrial Science and Medicine (“ISM”) communications band around afrequency of 2.45 Ghz. The ISM band actually extends from 2.4 Ghz to2.480 Ghz and includes 79 communication channels or sub-ranges offrequency, on which devices may communicate.

[0002] Many other types of devices operating according to applicablestandards also operate on the various channels within the ISM band. Forinstance, Wireless Local Area Network (“WLAN”) devices (also based onthe IEEE 802.11b standard) operate in the ISM. Devices operatingaccording to the WLAN standard are designed to replace a wired LANinfrastructure. Other types of devices that operate in the ISM bandinclude microwaves, various types of monitoring devices such as babymonitors, etc.

[0003] Very recently, the IEEE Standards Board adopted a newcommunications standard, IEEE 802.15.1, known as “Wireless MAC and PHYSpecifications for Wireless Personal Area Networks (WPANs™)”. Thisstandard closely mirrors the Bluetooth standard. Adoption of such astandard by the widely-recognized IEEE Standards Board means thatwireless devices designed to operate in wireless personal area networksare even more likely to model their operation on this standard. Unlessotherwise noted, where specific features or requirements of theBluetooth standard and Bluetooth devices are discussed below, those samefeatures or requirements are present in the IEEE 802.15.1 standard.

[0004] As enabling technologies advance and as standards are developedand adopted, wireless networks and the communications and otherapplications running thereon, are expected to become more and moreprevalent. This area of technology is expected to experience explosivegrowth over the next several years. Even before the recent standardadoption by the IEEE, it was forecast that by the year 2004 there willbe over 100 million Bluetooth devices in the United States alone andover 400 million worldwide.

[0005] One problem associated with all types of wireless communicationsis that signals being transmitted by different devices at the samefrequency can interfere with one another. This can be referred to asco-channel interference when it occurs between devices operating in thesame ISM channel. Interference can also occur between devices operatingat frequencies which are not the same but which are close to oneanother. For devices operating in adjacent ISM channels, this can bereferred to as adjacent interference. Both types of interference cancause communication packets to be lost, garbled or misinterpreted by thereceiving device, hindering the practical speed and accuracy of thewireless communications.

[0006] In an attempt to minimize the incidence of serious interference,the Bluetooth standard calls for Bluetooth devices to “hop” on all 79channels within the ISM band. That is, the devices transmit only acertain amount of data on a channel before moving to another channel tocontinue transmitting. The standard establishes the criteria forhopping—how much data to transmit on each channel, when to hop and theorder in which to hop to each channel. Devices following the standardunderstand these criteria and are able to establish and maintaincommunications with one another while hopping from channel to channel.Because of the advantages of hopping from channel to channel whiletransmitting, it is likely that other, non-Bluetooth devices willimplement this strategy for avoiding interference.

[0007] The Bluetooth standard calls for re-transmitting packets whendata is lost in transmission, typically due to interference. Theprocedure for re-transmitting increases transmission time and degradesthe data rate. In many of the applications to which Bluetooth devicesare applied, such as voice transmissions over IP (internet protocol),even the smallest degradation in the data rate is unacceptable becausethe quality of the signal quickly degrades to an unusable state.

[0008] Unlike Bluetooth devices, WLAN devices, and most other devicesoperating in the ISM band, select one static channel and transmit dataonly on that channel. Because they are designed to operate over agreater distance than Bluetooth devices, WLAN devices transmit much morepowerful signals. Therefore, Bluetooth device signals can experienceserious interference problems when hopping to a channel upon which aWLAN device is transmitting, or to an adjacent channel. As Bluetooth andWLAN devices, and other types of devices operating in the ISM band,become more and more popular, the prevalence of this type ofinterference will increase. The resulting degradation in performancewill seriously hinder customer acceptance of this emerging technology.

[0009] For these reasons, and others readily identified by those skilledin the art, it would be desirable to develop communications techniquesapplicable to the Bluetooth (and IEEE 802.15.1) standard, and to thecommunication protocols of any other wireless devices which hop fromchannel to channel while transmitting, which will minimize the effectson performance of any interference due to the transmission signals ofother devices in the ISM band.

SUMMARY OF THE INVENTION

[0010] The present invention contemplates a method whereby a wirelessdevice communicating according to certain communications standards mayeliminate or mitigate the effects on the communication rate ofinterference from other wireless communications signals. The presentinvention is applicable to wireless devices operating according to anycommunications standard which requires that the device hop fromcommunications channel to communications channel within a definedcommunication frequency band. This method does not require changes tothe standards definitions nor does it require any modifications to thereceiving device. In realizing these and other purposes of the presentinvention, a communications method calls for a wireless device to scanthe channels of the applicable communications frequency band andidentify any channel where other device(s) are transmitting and causinginterference. When the wireless device hops to one of the channelsidentified as experiencing interference, the device transmits only nullpacket(s) on that channel instead of data packet(s). Normalcommunications transmission is continued when the device hops to achannel which has not been identified as experiencing interference.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Some of the purposes of the invention having been stated, otherswill appear as the description proceeds, when taken in conjunction withthe accompanying drawing, in which:

[0012]FIG. 1 is a figurative illustration of the ISM communicationsfrequency band showing a WLAN device transmitting on one channel.

[0013]FIG. 2 is a simple representation of a wireless communicationsdevice according to the present invention, showing one possible methodof marking channels which are experiencing interference.

[0014]FIG. 3 is a figurative illustration of a wireless communicationsdevice according to the present invention transmitting data.

[0015]FIG. 4a is a flow-chart of a first embodiment of the method of thepresent invention.

[0016]FIG. 4b is a flow-chart of a second embodiment of the method ofthe present invention.

[0017]FIG. 4c is a flow-chart of a third embodiment of the method of thepresent invention.

[0018]FIG. 4d is a flow-chart of a fourth embodiment of the method ofthe present invention.

DETAILED DESCRIPTION

[0019] While the present invention will be described more fullyhereinafter with reference to the accompanying drawings, in which apreferred embodiment(s) of the present invention is shown, it is to beunderstood at the outset of the description which follows that personsof skill in the appropriate arts may modify the invention here describedwhile still achieving the favorable results of the invention.Accordingly, the description which follows is to be understood as beinga broad, teaching disclosure directed to persons of skill in theappropriate arts, and not as limiting upon the present invention.

[0020] Devices capable of wireless communications according to theBluetooth, IEEE 802.15.1 and other standards and the various methods andtechnologies employed by such devices to transmit and receive data arewell known to persons skilled in the relevant arts. Such devices may beimplemented in any of the many alternate embodiments that are availablewithout departing from the spirit of the present invention. Detaileddescriptions of such devices and technologies are not required for anunderstanding of the present invention. This invention relates only toan improvement to the method of operation of such devices.

[0021] In accordance with this invention, a device capable of wirelesscommunication over one or more channels within a defined frequency band,such as a Bluetooth device, for example, is provided with the capabilityof scanning the available channels and identifying any channels on whichother devices are transmitting. FIG. 1 illustrates the ISMcommunications band 100 with its various communications channels 110. AWLAN device (not shown), for example, transmitting communicationspackets 130 on one of the channels, identified as channel 3 for purposesof illustration. In this example, channel 3 would be identified asexperiencing interference.

[0022] A Bluetooth device practicing the communications method accordingto the present invention includes the capability to maintain a record ofwhich channel(s) have been so identified at least as long as the deviceis powered on and operating. With reference to FIG. 2, this might beaccomplished using a simple array 160 stored in a local volatile ornon-volatile memory module 170 of the communicating device 180. Thearray could include an entry 190 for each available channel whose value(0 or 1, for example) could indicate whether the associated channel wascurrently identified as experiencing interference. The device couldalternatively maintain a record of channels identified as experiencinginterference in any one of the many other ways such information isstored and accessed in electronic devices, as well understood by thoseskilled in the relevant arts.

[0023] As discussed above, a communications device according to thepresent invention hops from channel to channel while transmitting data.When practicing the method of the present invention, the device checksits record of channels experiencing interference each time it hops. Ifit is hopping to a channel currently marked as experiencinginterference, only null packets, that is, packets containing no data,are transmitted on such channel. If it is hopping to a channel that isnot currently marked as experiencing interference, normal data packetsare transmitted. In this way, the device avoids the need to re-transmitpackets which are lost or garbled due to being transmitted on channelsexperiencing interference. Since the device knows that only null packetswere transmitted on those channels, any packets lost or garbled on thosechannels can simply be ignored.

[0024] Referring now to FIG. 3, a communicating device according to thepresent invention is (not shown) transmitting data packets 200 on thevarious available communications channels 110 in the manner called forby the Bluetooth and similar standards. As described in the exampleabove, channel 3 has been identified as experiencing interference from atransmitting WLAN device. As such, when hopping to channel 3, the deviceaccording to the present invention only transmits a null packet(s) 210,and continues transmitting data packets 200 when the transmission moveson to other channels.

[0025] In one embodiment of the present invention, a wirelesscommunications device practicing the method of the present inventionautomatically scans the available communications channels upon power up,marking those channels experiencing interference. This embodiment of thepresent method is illustrated in FIG. 4a. In another embodiment, awireless communications device practicing the method of the presentinvention would not automatically scan the channels at power up.Instead, scanning would be initiated only if the communications datarate dropped below a certain level. The threshold data rate could beuser-configurable or could be set at manufacture. In any event, thethreshold would be set at a point where it is apparent that interferenceis seriously impacting the effective data rate. This embodiment of thepresent method is illustrated in FIG. 4b.

[0026] A third embodiment calls for a wireless communications devicepracticing the method of the present invention to initiate a scan of thechannels for interference only when manually triggered to do so by auser. This embodiment of the present method is illustrated in FIG. 4c.Finally, a fourth embodiment requires that the wireless communicationsdevice practicing the method of the present invention perform thechannel scan after the passage of a certain time period. This embodimentof the present method is illustrated in FIG. 4d. Again, the time periodcould be user-configurable or could be set at manufacture. This wouldinsure that the channels marked as experiencing interference wouldremain accurate and up-to-date.

[0027] These embodiments of the present method can also be used incombination. A wireless communications device of the present inventioncould scan for channels experiencing interference upon power up. Then,if the wireless communications data rate were to fall below a certainrate, the device could initiate a new scan to determine if different oradditional channels were experiencing interference. Or, a new scan couldbe initiated after each passage of a certain amount of time. This wouldavoid the situation where the device continues sending null packets on achannel marked as experiencing interference long after the markedchannel ceased experiencing interference. On top of all that, the devicecould allow a user to initiate a new scan at any time through some typeof user input interface.

[0028] As readily recognized by those skilled in the art, the exactorder of the method steps illustrated and discussed herein may be variedin any advantageous manner without deviating from the present invention.Also, where appropriate, steps may be repeated, skipped or combined tobetter operate in a given environment.

[0029] In the drawings and specification there has been set forthpreferred embodiments of the invention, and, although specific terms areused, the description thus given uses terminology in a generic anddescriptive sense only and not for purposes of limitation.

1. in a wireless communications system providing for communication overtwo or more channels utilizing a communications architecture that callsfor hopping from channel to channel during data transmission, a methodfor mitigating the effects of interference, the method comprising:scanning the channels for interference and identifying channelsexperiencing interference; transmitting only null packets when hoppingto a channel identified as experiencing interference; transmittingnormal data when hopping to a channel not identified as experiencinginterference.
 2. The method of claim 1 wherein the scanning step isperformed upon the commencement of data transmission.
 3. The method ofclaim 1 wherein the scanning step is performed upon each passage of afirst time period.
 4. The method of claim 2 wherein the scanning step isrepeated periodically during data transmission.
 5. The method of claim 1wherein the scanning step is performed when a data throughput rate fallsbelow a predefined value.
 6. The method of claim 1 wherein the scanningstep is performed when requested by a user.
 7. The method of claim 2wherein the scanning step is repeated whenever: a) a second time periodhas passed: b) a data throughput rate falls below a predefined value; orc) requested by a user.
 8. The method of claim 1 wherein thecommunication architecture is the standard known as Bluetooth.
 9. Themethod of claim 1 wherein the communication architecture is the standardknown as IEEE 802.15.1.
 10. The method of claim 7 wherein thecommunication architecture is the standard known as Bluetooth.
 11. 1)Themethod of claim 7 wherein the communication architecture is the standardknown as IEEE 802.15.1.
 12. In a wireless communications systemproviding for communication in the ISM communications frequency band bya communications device operating according to the Bluetooth standard, amethod for mitigating the effects of interference, the methodcomprising: upon power up of the device, scanning the available channelsfor interference and identifying channels experiencing interference;transmitting only null packets when hopping to a channel identified asexperiencing interference; transmitting normal data when hopping to achannel not identified as experiencing interference.
 13. The method ofclaim 12 wherein the scanning step is repeated periodically during datatransmission.
 14. The method of claim 12 wherein the scanning step isrepeated when a data throughput rate falls below a predefined value. 15.The method of claim 12 wherein the scanning step is repeated whenrequested by a user.
 16. The method of claim 12 wherein the scanningstep is repeated whenever: a) a third time period has passed; b) a datathroughput rate falls below a predefined value; or c) requested by auser.
 17. In a wireless communications system providing forcommunication in the ISM communications frequency band by acommunications device operating according to the IEEE 802.15.1 standard,a method for mitigating the effects of interference, the methodcomprising: upon power up of the device, scanning the available channelsfor interference and identifying channels experiencing interference;transmitting only null packets when hopping to a channel identified asexperiencing interference; transmitting normal data when hopping to achannel not identified as experiencing interference.
 18. The method ofclaim 17 wherein the scanning step is repeated when a data throughputrate falls below a predefined value.
 19. The method of claim 17 whereinthe scanning step is repeated when requested by a user.
 20. The methodof claim 17 wherein the scanning step is repeated whenever: a) a fourthtime period has passed; b) a data throughput rate falls below apredefined value; or c) requested by a user.